This invention is related in general to the field of manufacturing heterogeneous integrated circuit devices utilizing bonded single-crystal films. More particularly, the invention is related to a method for detaching thin single-crystal films from crystal for bonding onto growth-incompatible substrates.
Epitaxial liftoff techniques have been used since 1987 for achieving heterogeneous integration of many III-V and elemental semiconductor integrated circuits. For example, epitaxial liftoff has been shown to be effective for integrating hetero-junction bipolar transistors (HBT""s) and diode lasers on silicon, gallium arsenide and other common substrates. Despite this success, however, it has been impossible to integrate devices comprised of other important materials, namely non-semiconductor materials such as metal oxides, on these common substrates.
A need for integrated circuit devices combining non-semiconductor materials with conventional substrates has arisen in the field of electro-optic and magneto-optic devices. For example, a need has arisen for on-chip integrated magneto-optical devices, such as optical isolators, for use in fiber-optic telecommunications networks. Although commercially available isolators use bulk bismuth-substituted yttrium iron garnet (Bixe2x80x94YIG), and other conventional integrated isolators require epitaxial growth on gadolinium gallium garnet (GGG), conventional epitaxial growth technologies are subject to the limitations of high temperature chemistry, complex stoichiometry and lattice matching.
More importantly, conventional methods are ineffective for growing single crystal-structures that exhibit good optical and magnetic properties for combination with semiconductor materials. Efforts using sputter growth technology, for example, have been unsuccessful in yielding single-crystal films with acceptable optical and magnetic properties.
Another need for integrated circuit devices combining non-semiconductor materials with conventional substrates has arisen in the field of microwave communications. For example, the need has arisen for frequency agile resonators requiring integrated circuit devices. Conventional frequency agile resonators, made of poly-crystalline materials such as ferroelectric solids, are undesirable because of their limited bandwidth and high loss tangents. Instead, it is desirable to construct frequency agile resonators and other integrated microwave circuits which are made of ferroelectric or magneto-optic single-crystal films.
Furthermore, conventional epitaxial liftoff techniques as developed for III-V semiconductors make use of the large differential etch rates between a buried sacrificial layer and the epitaxial structure of interest to detach the latter from its growth substrate. For example, early epitaxial liftoff techniques were based on the high wet etch selectivity of an aluminum arsenide (AlAs) layer over an aluminum gallium arsenide (AlxGal-xAs) layer. Subsequent work has demonstrated the liftoff of epitaxially grown layers in other III-V materials, all based on selective etching of sacrificial epitaxial layers. In addition, conventional ion-implantation-based epitaxial liftoff techniques, albeit using different separation mechanisms have been reported in high-dose-high-energy O-implanted diamond and H-implanted Si. See xe2x80x9cSingle-Crystal Diamond Plate Liftoff Achieved by Ion Implantation and Subsequent Annealing,xe2x80x9d N. R. Parikh, J. D. Hunn, E. McGucken, M. L. Swanson, C. W. White, R. A. Ruder, D. P. Malta, J. B. Posthill and R. J. Markunas, Appl. Phys. Lett. 61 (26), Dec. 28, 1992; M. Bruel, Electron. Lett., vol. 31 at 1201 (1995). Conventional bonding techniques for epitaxially grown layers have included the use of adhesives and van der Waals forces on bare substrates.
Therefore, it is an object of the present invention to provide a method for detaching thin single-crystal films from crystal, such as epilayer/substrate or bulk single-crystal material, for bonding onto growth-incompatible substrates.
It is another object of the present invention to provide a method for detaching thin single-crystal films made of magnetic garnet materials from growth-compatible substrates for use in integrated photonics and microwave circuits.
It is still another object of the present invention to provide a method for detaching thin single-crystal films made of ferroelectric materials from growth-compatible substrates or bulk crystal for use in integrated photonics and microwave circuits.
It is yet another object of the present invention to provide a method for detaching thin single-crystal films from growth-compatible substrates without using conventional etching techniques.
It is a further object of the present invention to provide a method for enhancing the etch selectivity and detachment of thin single-crystal films from bulk crystal.
Hence, crystal ion-slicing methods are hereinafter described that substantially overcome the aforedescribed limitations and inadequacies of conventional epitaxial lift-off methods. In a preferred method of the present invention, for example, a method is provided for detaching a single-crystal film from crystal. The crystal, for example, can be an epilayer/substrate crystal or a bulk crystal. The method includes the steps of implanting ions into the crystal structure to form a damage layer within the crystal structure at an implantation depth below a planar top surface of the crystal structure, and then chemically etching the damage layer to effect detachment of the single-crystal film from the crystal structure. The preferred method of the present invention is especially useful for detaching single-crystal metal oxide films from metal oxide crystal structures.
In accordance with another preferred method of the present invention, a method is provided for detaching a single-crystal film from a crystal structure, the method including the steps of implanting ions into the crystal structure to form a damage layer within the crystal structure at an implantation depth below a planar top surface of the crystal structure, and then subjecting the crystal structure with the damage layer to a rapid temperature increase to effect detachment of the single-crystal film from the growth-compatible substrate without chemical etching.
In accordance with yet another preferred method of the present invention, a method is provided for detaching a single-crystal film from a crystal structure, the method including the steps of implanting ions into the crystal structure to form a damage layer within the crystal structure at an implantation depth below a planar surface of the crystal structure, bonding the crystal structure to a second substrate, and subjecting the crystal structure with the damage layer to a rapid temperature increase to effect detachment of the single-crystal film from the crystal structure without chemical etching. Where the crystal structure is a metal oxide, such as LiNbO3, and the second substrate is a semiconductor substrate, such as silicon or gallium arsenide, bonding of the crystal structure to the semiconductor substrate may be achieved by polishing, where necessary, and cleaning the ion implanted surface of the crystal structure and cleaning the bonding surface of the semiconductor substrate, which is polished and flat. The ion implanted surface of the crystal structure is then placed in contact with the bonding surface of the semiconductor substrate, and the crystal structure and the semiconductor substrate are heated to a moderately high temperature, such as 100xc2x0 C., for a moderately long interval of time, such as 15 minutes, to effect bonding between the implanted surface of the crystal structure and the bonding surface of the semiconductor substrate. The ion implanted crystal structure bonded in this manner to the semiconductor substrate is then subjected to a rapid temperature increase to effect detachment of the single-crystal film from the crystal substrate without chemical etching and with the detached single-crystal film remaining bonded to the semiconductor substrate.
Further, a method for enhancing the detachment of a single-crystal film from a bulk crystal structure is provided, the method including the steps of: implanting ions into the bulk crystal structure to form a damage layer at an implantation depth below a planar top surface of the bulk crystal structure; rapid thermal annealing the ion-implanted bulk crystal structure; and chemically etching the damage layer within the annealed bulk crystal structure to effect detachment of the single-crystal film from the bulk crystal structure.
Still further, a method is provided for enhancing the etch selectivity as between a bulk crystal structure and an ion implantation damage layer formed in the bulk crystal structure, the method including the steps of implanting ions into the bulk crystal structure to form a damage layer at an implantation depth below a planar top surface of the bulk crystal structure; and rapidly thermal annealing the ion-implanted bulk crystal structure.
Yet further, a method is provided for enhancing the detachment of a single-crystal film from a ferroelectric bulk crystal structure, the method including the steps of: implanting ions into the bulk crystal structure to form a damage layer at an implantation depth below a planar top surface of the bulk crystal structure; rapid thermal annealing the ion-implanted bulk crystal structure; and chemically etching the damage layer within the annealed bulk crystal structure to effect detachment of the single-crystal film from the bulk crystal structure.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.